全文获取类型
收费全文 | 1323篇 |
免费 | 54篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 10篇 |
综合类 | 1篇 |
化学工业 | 407篇 |
金属工艺 | 46篇 |
机械仪表 | 29篇 |
建筑科学 | 5篇 |
矿业工程 | 2篇 |
能源动力 | 79篇 |
轻工业 | 115篇 |
水利工程 | 5篇 |
石油天然气 | 10篇 |
无线电 | 78篇 |
一般工业技术 | 394篇 |
冶金工业 | 98篇 |
原子能技术 | 7篇 |
自动化技术 | 93篇 |
出版年
2024年 | 5篇 |
2023年 | 18篇 |
2022年 | 34篇 |
2021年 | 39篇 |
2020年 | 41篇 |
2019年 | 27篇 |
2018年 | 54篇 |
2017年 | 50篇 |
2016年 | 42篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 101篇 |
2012年 | 92篇 |
2011年 | 103篇 |
2010年 | 59篇 |
2009年 | 59篇 |
2008年 | 58篇 |
2007年 | 65篇 |
2006年 | 34篇 |
2005年 | 34篇 |
2004年 | 20篇 |
2003年 | 30篇 |
2002年 | 24篇 |
2001年 | 12篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 26篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 17篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 11篇 |
1974年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有1379条查询结果,搜索用时 15 毫秒
1.
Semiconducting molybdenum trioxide thin films have been prepared by employing simple and inexpensive spray pyrolysis technique.
Films are found to be polycrystalline in nature with hexagonal phase. Optical band gap energy (direct) and room temperature
electrical resistivity are of the order of 2·9 eV and 108 ohm-cm, respectively. These films exhibit cathodic electrochromism. 相似文献
2.
3.
The temporal scale effect of loading data on nitrate-nitrogen load computation was examined using outputs of watershed modeling tool Hydrologic Simulation Program-FORTRAN (HSPF) for the Amite River in Louisiana, USA. The daily nitrate-nitrogen concentrations simulated using the HSPF were employed first to obtain daily, weekly, bi-weekly, and monthly average data and then to develop load duration curves for the data with four different temporal scales. The duration curves exhibited high variability in the load estimated using daily data as compared with those based on bi-weekly and monthly data. According to daily data, the nitrate-nitrogen load in the winter was found to be 2,780 kg. The nitrate-nitrogen load decreased with increasing temporal (daily, weekly, bi-weekly, and monthly) scale (commonly used in water quality monitoring) of the data. The coefficient of variation, used to quantify the effect of temporal scale on the load, was found to be linearly and inversely correlated with the logarithm of the time scale. Based on the finding, empirical equations were proposed to extrapolate near real-time data for flow and nitrate-nitrogen, greatly simplifying nutrient monitoring and reducing the cost involved in water quality monitoring. 相似文献
4.
Shruti V. Patil Ramesh B. Kasetti J. Cameron Millar Gulab S. Zode 《International journal of molecular sciences》2022,23(13)
Glaucoma is a multifactorial disease leading to irreversible blindness. Primary open-angle glaucoma (POAG) is the most common form and is associated with the elevation of intraocular pressure (IOP). Reduced aqueous humor (AH) outflow due to trabecular meshwork (TM) dysfunction is responsible for IOP elevation in POAG. Extracellular matrix (ECM) accumulation, actin cytoskeletal reorganization, and stiffening of the TM are associated with increased outflow resistance. Transforming growth factor (TGF) β2, a profibrotic cytokine, is known to play an important role in the development of ocular hypertension (OHT) in POAG. An appropriate mouse model is critical in understanding the underlying molecular mechanism of TGFβ2-induced OHT. To achieve this, TM can be targeted with recombinant viral vectors to express a gene of interest. Lentiviruses (LV) are known for their tropism towards TM with stable transgene expression and low immunogenicity. We, therefore, developed a novel mouse model of IOP elevation using LV gene transfer of active human TGFβ2 in the TM. We developed an LV vector-encoding active hTGFβ2C226,228S under the control of a cytomegalovirus (CMV) promoter. Adult C57BL/6J mice were injected intravitreally with LV expressing null or hTGFβ2C226,228S. We observed a significant increase in IOP 3 weeks post-injection compared to control eyes with an average delta change of 3.3 mmHg. IOP stayed elevated up to 7 weeks post-injection, which correlated with a significant drop in the AH outflow facility (40.36%). Increased expression of active TGFβ2 was observed in both AH and anterior segment samples of injected mice. The morphological assessment of the mouse TM region via hematoxylin and eosin (H&E) staining and direct ophthalmoscopy examination revealed no visible signs of inflammation or other ocular abnormalities in the injected eyes. Furthermore, transduction of primary human TM cells with LV_hTGFβ2C226,228S exhibited alterations in actin cytoskeleton structures, including the formation of F-actin stress fibers and crossed-linked actin networks (CLANs), which are signature arrangements of actin cytoskeleton observed in the stiffer fibrotic-like TM. Our study demonstrated a mouse model of sustained IOP elevation via lentiviral gene delivery of active hTGFβ2C226,228S that induces TM dysfunction and outflow resistance. 相似文献
5.
P.P. Hankare M.R. Kadam P.D. Kamble S.D. Jadhav U.B. Sankpal R.P. Patil V.B. Helavi N.S. Gajbhiye 《Journal of Alloys and Compounds》2010,489(1):233-236
The system manganese substituted lanthanum ferrite viz. LaMnxFe1?xO3 (1.0 ≤ x ≥ 0) was prepared by sol–gel autocombusion method. The structural characterization of the samples was carried out by X-ray diffraction technique and it is found that, the phase transfer from cubic to orthorhombic perovskite structure. The lattice parameter and crystallite size decrease with increasing Mn content. The phase formation of perovskite was revealed by thermal analysis technique. The surface morphology and elemental analysis of all the samples were carried out by scanning electron microscopy and energy dispersive X-ray spectroscopic technique, respectively. Electrical properties of the compounds show that, they exhibit semiconducting behavior. The substitution of manganese ions plays an important role in changing their structural, electrical and magnetic properties of lanthanum ferrite. 相似文献
6.
Nilesh Ganpatrao Patil P. K. Brahmankar 《The International Journal of Advanced Manufacturing Technology》2010,51(5-8):599-610
Wire electro-discharge machining (WEDM) is a vital process in manufacturing intricate shapes. The present work proposes a semi-empirical model for material removal rate in WEDM based on thermo-physical properties of the work piece and machining parameters such as pulse on-time and average gap voltage. The model is developed by using dimensional analysis and non-linear estimation technique such as quasi-Newton and simplex. Predictability of the proposed model is more than 99% for all work materials studied. The work materials were silicon carbide particulate reinforced aluminium matrix composites. The experiments and model prediction show significant role of coefficient of thermal expansion in WEDM of these materials. In addition, an empirical model, based on response surface method, has also been developed. The comparison of these models shows significant agreement in the predictions. 相似文献
7.
The recent explosion in multimedia and networking application places a great demand on efficient transmission of images at
low bit rate with high security. Mixing several existing standard encryption techniques with image encoding tends to change
the compression ratio greatly. In this paper, a novel image encryption algorithm is embedded as a part of JPEG image encoding
scheme to meet three major necessities: (1) to provide temporal security against casual observer, (2) to preserve the compression
ratio, (3) remain compliant with the JPEG file format. In the proposed algorithm, the modified DCT blocks are confused by
a fuzzy PN sequence. In addition to that, the DCT coefficients of each modified DCT block are converted to unique uncorrelated
symbols, which are confused by another fuzzy PN sequence. Finally, the variable length encoded bits are encrypted by chaotic
stream cipher. An amalgamation of all the three techniques with random combination of seeds will provide the required security
against the casual listener/observer where the security needed is only in-terms of few hours. 相似文献
8.
We study reducing feedback overhead of users' channel state information required for opportunistic scheduling at a base station while minimizing the throughput penalty incurred due to reduced feedback. We first propose a simple contention based scheme known as 'static splitting' for best effort traffic. The idea is to divide users into static groups, with users that belong to a group, and have their currently supported rate above a threshold, contending to send their current feedback to the base station. This is combined with maximum quantile scheduling -scheduling a user whose current rate is high relative to its distribution, to obtain thresholds that are independent of users' rate distributions even when they are heterogeneous, allowing off-line optimization of thresholds. Next we develop the insight that for a traffic mixture of best effort and real-time traffic one has to combine contention and polling to reduce feedback while providing quality of service. We propose a scheme based on this insight. Under this scheme we prove a lower bound on the service seen by a real-time when users' channel capacities are fast fading. Furthermore, we propose a heuristic modification that is able to exploit a larger fraction of opportunism. Simulation results illustrate the performance advantage of the proposed schemes. 相似文献
9.
Patwardhan P.G. Patil B. Gadre V.M. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2007,54(9):790-794
In this brief, we derive conditions on the polyphase matrix of 2-D finite-impulse response (FIR) quincunx filter banks, for the filters in the filter bank to have quadrantal or diagonal symmetry. These conditions provide a framework for synthesizing polyphase structures which structurally enforce the symmetry. This is demonstrated by constructing examples of small parameterized matrix structures which satisfy the above conditions, thus giving perfect reconstruction FIR quincunx filter banks with quadrantal or diagonally symmetric short-kernel (i.e., short-support) filters. It is also shown that cascades of the above constructed small structures can be used to construct filters of higher order. 相似文献
10.
Sanjeev Kumar Pandey S. L. Patil Praveen V. Pol S. B. Phadke 《International Journal of Electronics》2020,107(10):1682-1703
ABSTRACT In this paper, two control schemes for boost converters affected by uncertainties in input voltage and load are proposed. The boost converter dynamics is redefined in terms of new state variables to facilitate the use of a disturbance observer that can estimate matched and unmatched disturbances. A sliding surface, which is new in the context of boost converters, is proposed to enable tracking and regulation of output voltage without requiring measurement of input voltage and load current. The stability of the overall system including the disturbance observer, the sliding variable and the output is proved. The performance of the schemes is assessed for regulation of output voltage and tracking of reference voltage by simulation as well as experimentation in which various types of uncertainties and various types of reference voltages are considered. 相似文献